Electronic devices need power for their operation. This power may be delivered internally, for example from a battery, or externally, for example from a power supply. An external power supply may be a unit designed with the primary purpose of providing power, or the external power supply may be part of another electronic device. For example, a laptop computer may include a power supply that provides power to a portable media device. Power provided by an external supply may be provided over a cable or other electrical conductor. These cables may have connectors on each end that may mate with connectors on the power supply and the electronic device that is receiving the power. These cables may provide only power, or they may provide power and data. Data may be provided over wire conductors, fiber optic conductors, or other types of conductors in the cables.
These power supplies and electronic devices may be located near each other in a relatively benign environment. For example, the above laptop and portable media player may be located near each other on an office desk. But in other situations, the devices may be more remote from each other. In these or other situations, there may be a less benign environment between external power supply and the electronic device. In these situations, a cable providing power from a power supply to an electronic device may be routed over a long distance, it may be routed through a harsh environment, it may be routed through a path where damage is likely, or it may be routed through another potentially hazardous path.
This routing may lead to concerns about the physical limitations of the cable being used. For example, a cable may have a maximum current above which localized heating may damage the cable. The potential for this or other damage that may be caused by these hazardous pathways may lead to safety concerns for the power supply, the electronic device being powered, and third parties. These safety concerns may implicate regulatory aspects as well.
Thus, what is needed are circuits, methods, and apparatus that may provide power supply voltages in a safe and reliable manner that meets these safety and regulatory concerns and does not exceed physical limitations of cables and other circuits and components used to provide the power supply voltages.